This invention relates to a pneumatically or hydraulically powered metal shearing mechanism and, more particularly, to an improved shearing mechanism adapted for connection to a boom of an excavator or similar machine for in situ severing of metal products.
Conventional powered metal shearing mechanisms or shears have a pivotable and a fixed shear or jaw each with cutting surfaces. The terms "jaw" and "blade" are used interchangeably herein. Typically, the top one of the jaws pivots about a transverse connecting pin and severs material placed between the jaws. Typically applications for these devices are for demolition to clear and reclaim rubble.
A drawback with many devices of this type is that when one jaw is pivoted towards the second jaw to cut the material, the jaws tend to separate in a direction transverse to the direction of shearing. This separation often results in warping, rolling and/or breaking of one of the jaws or the connecting pin, thereby limiting the size and strength of material that can be severed with a particular size of shear as well as detrimentally effecting the life expectancy of a shear which is operated beyond such limits.
Examples of shearing devices that have tried to alleviate shear separation are described in U.S. Pat. Nos. 4,543,719,; 4,558,515, and 4,776,093. These devices attempt to solve the problem associated with shear separation by providing a second parallel, non-cutting jaw adjacent a first non-movable or fixed jaw. The movable jaw crushes the material between the second non-cutting jaw and the fixed jaw. However, a drawback to these devices is that the material may often lodge in between the non-cutting jaw and the adjacent cutting jaw and must later be pushed out resulting in an interruption of the shearing operations. Further, these shearing devices waste available cutting force because the force of the moving shear is directed into deforming or dragging the material mass against or through the non-cutting or second jaw and the first non-movable jaw.
Another drawback to prior shearing devices is that when severing the mass the moveable jaw tends to separate from the first non-moveable cutting jaw. Separation between the shear jaws while cutting may reduce the effective shearing force and may reduce the life expectancy of the shears.
One solution to the aforementioned drawbacks is the shearing device described in Applicant's prior U.S. patent application Ser. No. 07/871,023 filed Apr. 20, 1992. This shearing device has an outrigger attached to a fixed jaw. The outrigger has a surface at a preset angularly spaced relationship to the cutting plane of the fixed jaw so that when the movable jaw engages material laying across the outrigger and the fixed jaw, loading on the outrigger creates a torque on the fixed jaw. The fixed jaw responds to this torque by urging its cutting surface toward the movable jaw.
When shearing certain high-strength materials, it has been found that a welded connection between the outrigger and the fixed jaw is not always of sufficient strength to withstand the shear loading. Consequently, when shearing some thick materials, the outrigger may fail. Furthermore, torque loading on a pivot pin connecting the movable jaw to the fixed jaw may also become unusually severe. As the shears sever a mass, such severe torque loading may result in warping of the connecting pin, thereby reducing the shearing device structural integrity and potentially resulting in pin breakage or shear separation. A reduction in structural integrity also decreases the shearing device effectiveness in severing material.